The present disclosure relates to a synthetic test circuit for testing a thyristor valve in a high voltage direct current (HVDC) system.
High voltage direct current (HVDC) transmission is one of electricity transmission methods. According to the HVDC transmission, a high voltage AC power generated in a power plant is converted into a high voltage DC power having relatively high efficiency by using a power inverter to transmit the high voltage DC power. Thereafter, the transmitted high voltage DC power is converted again into the AC power by the power inverter to transmit the AC power. The HVDC transmission may have an advantage in long-distance transmission because of relatively low power consumption.
The power inverter used for the HVDC transmission may be divided into a thyristor-based current source inverter and an insulated gate bipolar mode transistor (IGBT)-based voltage source inverter according to a shape of a valve. The current source inverter is being commonly used from the 1980s until now. On the other hand, the voltage source inverter became commercialized in the early 2000s. Thereafter, although the voltage source inverter continuously increases in capacity, the capacity of the voltage source inverter is still less than that of the current source inverter. Thus, the voltage source inverter is being mainly utilized for connecting a large scale offshore wind power plant to an AC power grid.
In the HVDC transmission, one of the most important factors is an AC-DC and DC-AC power inverter. Since the power inverter has a very high operation voltage, a plurality of thyristors are connected to each other in series to constitute one valve. It is necessary to verify operations of the valves through a voltage and power to be applied when operating before the power inverter is installed. However, to verify the operations of the valves through the voltage and power to be applied when operating, a huge power may be consumed, and security problems may occur.
Thus, an apparatus for simulating the operation voltage and capacity of the power inverter to test the valves is needed. This apparatus is called a synthetic test circuit. The synthetic test circuit includes a current generation unit for supplying forward current to be applied when the valve is turned on and a voltage generation unit for supplying a reverse voltage and forward voltage to be applied when the valve is turned off.